igneous
Porphyritic Basalt or Porphyritic Andesite
Porphyritic extrusive igneous rock
AI-generated identification · may be incorrectHardness of 6-7 on the Mohs scale, dark gray or brown matrix with distinct lighter plagioclase feldspar phenocrysts, dull to sub-vitreous luster, and an aphanitic to phaneritic crystal structure.
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Physical properties
Hardness of 6-7 on the Mohs scale, dark gray or brown matrix with distinct lighter plagioclase feldspar phenocrysts, dull to sub-vitreous luster, and an aphanitic to phaneritic crystal structure.
Formation & geological history
Formed through a two-stage cooling process where magma begins cooling slowly deep underground, creating larger crystals, before erupting to the surface to cool rapidly.
Uses & applications
Used primarily in construction, as crushed aggregate for roadbeds, and occasionally as decorative stone when polished.
Geological facts
The contrasting larger crystals, known as phenocrysts, are embedded in a finer-grained groundmass. This textural feature provides a visible timeline of the magma's cooling history.
Field identification & locations
Identify in the field by looking for distinct light-colored crystal grains floating within a dark, fine-grained volcanic rock background. Commonly found in ancient and active volcanic regions worldwide.
